Pulsed power has a number of military, industrial, and scientific applications, such as the production of X-rays and nuclear fusion. For most applications, a high-voltage capacitor bank is discharged for pulsed power production. Unfortunately, the energy storage density of a typical high-voltage capacitor is relatively low, especially if the capacitor is rated for repetitive operation.
Due to the limitations of high-voltage capacitor banks, there has been considerable effort toward developing pulsed power generators using stored inductive energy. There are a number of relatively low cost electrical power sources that have a relatively high energy storage density but need inductive energy storage for pulsed power generation. These electrical power sources include homopolar generators, compensated alternators, explosively-driven magnetic flux compressors, and electrolytic capacitors. An opening switch, however, is needed for obtaining pulsed power having a fast current rise from the inductive energy storage.
For example, to power a dense plasma focus with an explosive generator, a useful switch would interrupt a few mega-amperes in less than one microsecond and remain open for the 3 to 4 microsecond pulse delivered to the device. (Freeman et al., “Plasma Focus Experiments Powered by Explosive Generators,” LA-UR-83-1083, Los Alamos National Laboratories, Los Alamos, 1983, p. 13.)
Efforts toward development of a suitable opening switch are described in G. D. Roy, “High Power, High Repetition Rate Switches: An Overview,” Naval Research Review, Vol. 2, 1990, p. 17-24. Desired attributes of the switch are fast opening, fast recovery to achieve high repetition rates, controllable and long conduction time, low resistance during conduction, fast rise of impedance during opening, high impedance after opening, large currents, large stand-off voltage, and jitter-free operation. The plasma flow switch is mentioned as having conduction time up to 10−5 seconds and opening time in the 100 nanosecond time scale, and as of 1990, useful only in very high power (terawatt), low impedance (10 ohm), single shot, staged pulsed power systems. (Page 19.)
For repetitive operation of an inductive store employing homopolar generators, compensated alternators, or electrolytic capacitors, the opening switch should provide a closed state for at least about a millisecond. In this closed state, the voltage across the opening switch should be a small fraction of the voltage of the homopolar generator, compensated alternator, or capacitor bank in the inductive energy storage circuit.